A stereoscopic imaging device can be largely classified into a stereoscopic method and an autostereoscopic method.
The autostereoscopic method is a method of dividing left and right images spatially at a viewer's eye position and outputting the images. Representative examples of the autostereoscopic method include a lenticular method and a barrier method. The autostereoscopic method is very convenient because it does not use glasses, but has a phenomenon in which a stereoscopic image is interrupted when moving left and right and forward and rearward. The autostereoscopic method is also disadvantageous in that resolutions are inevitably lowered since a composed left and right image is output using one display.
The stereoscopic method is disadvantageous in that glasses serving as an optical filter must be worn, but is advantageous in that it is excellent in comparison with the autostereoscopic method in terms of the viewing angle or resolutions. Although stereoscopic imaging devices of various stereoscopic methods have been proposed, most of them use a polarization method. In the prior art, of the stereoscopic methods, a method in which position limits are relatively free, the highest resolution is supported, and two CRT monitors and a half mirror are used as shown in FIG. 1 was used a lot.
This method employs two CRT monitors one of which is for the left eye and the other of which is for the right eye. The method is configured to output picture signals captured by the CRT monitors and combine left and right images to the front through the half mirror, so that a stereoscopic image can be enjoyed using polarized glasses.
FIG. 1 is a view illustrating a construction of a conventional stereoscopic imaging device employing two CRT monitor.
Referring to FIG. 1, the conventional stereoscopic imaging device employing the two CRT monitors includes two CRT monitors 10, 20, polarization filters 11, 21 disposed in front of the CRT monitors 10, 20, respectively, and a half mirror 30 disposed at an angle of 45 degrees with respect to the front side of each of the monitors 10, 20 between the two CRT monitors 10, 20.
In the stereoscopic imaging device constructed above, the following two requirements must be met.
One of the requirements is that a phase difference of a polarization film adhered to each monitor must be 90 degrees, and the other of them is that an image mirror function for turning over left and right sides in order to correct an image must be implemented in an input signal stage because an image on a lower side is output by the half mirror with the left and right sides changed.
This method using the two monitors is advantageous in that a high-resolution stereoscopic image without image loss can be seen since left and right images are output from the respective monitor and combined in the space.
However, this method is disadvantageous in that it has a very large volume because the CRT monitors are used.
In order to supplement the disadvantage of the large volume due to the use of the conventional CRT monitors, a stereoscopic imaging device using two Thin Film Transistor Liquid Crystal Displays (TFT-LCD) having self-polarization filters attached thereto was proposed. The TFT-LCD is one of the widely used display devices in the field of flat displays since it enables direct IC driving because of low consumption power of several to several tens of □/□ and a low voltage operation and it is thin and light and can have a large-sized screen. However, most LCDs have the polarization filter attached thereto and are therefore problematic in that they do not satisfy the polarization orthogonality condition in which the phase difference of the polarization film attached to each monitor must be 90 degrees.
In order to solve the problems, applications regarding a variety of methods were filed. Japanese Patent Application no. 1996-116679 discloses a stereoscopic imaging device in which a liquid crystal display device having a polarization direction of a vertical axis x is a ‘normally white type’ and a liquid crystal display device having a polarization direction of a horizontal axis y is a ‘normally black type’.
The normally white type is of a type in which light can transmit in a normal state where voltage is not supplied to liquid crystal, and the normally black type is of a type in which light can transmit when voltage is supplied to liquid crystal.
The reason why different types of the liquid crystal display devices are used is that mutual perpendicularity could not be accomplished between types in which polarization directions of polarization filters in the existing liquid crystal display device are different. If different types of the liquid crystal display devices are used as described above, there are disadvantages in that a driving method is complicated and a lot of power consumption is needed because the two liquid crystal display devices must be switched in opposite directions. Furthermore, the normally white type and the normally black type have different output characteristics. For example, the normally black type has a low contrast ratio due to the occurrence of light leakage when a light source having a wide wavelength range is used as rear-surface light and therefore is problematic in that the picture quality of left and right images has a different characteristic.
As a method for solving the problem in which the picture quality of left and right images has a different characteristic, Korean Patent Application No. 1999-0049331 was filed. In this patent application, an attempt was made to prevent a reduction of a three-dimensional effect caused by the picture quality difference of left and right images, which occurs due to the use of LCD panels with different characteristics, so as to produce orthogonally polarized light. In other words, in order for polarization directions to be vertical to each other while using two sheets of the same normally black types as LCD panels, polarization filters on both sides of one of liquid crystal display devices is detached, and rotated 90 degrees in the same direction and then attached again.
However, this method is advantageous in that it uses the same panel, but cannot obtain an optimal design and performance of an original liquid crystal panel and, in even worse cases, may have a detrimental result in which an image output itself may become problematic because only the front and rear polarization filters are detached and then attached again at an angle of 90 degrees with no regard for the characteristics of the existing liquid crystal.
Further, there still remains a problem that image inversion must be performed although the polarization filters are attached again and used for the purpose of the orthogonal polarization condition.